This spinach mushroom breakfast casserole is an easy vegetarian egg bake with goat cheese. Perfect for brunch or holiday mornings. Get the recipe!

This spinach mushroom breakfast casserole has become my go-to for holiday mornings and lazy weekends alike. It’s essentially a giant frittata, eggs baked with sautéed mushrooms, wilted spinach, and tangy goat cheese. The vegetables give it a hearty texture while the goat cheese melts into creamy pockets throughout. Because it feeds a crowd (or provides leftovers for the week), it’s one of those dishes that solves breakfast without stress.

Why You’ll Love This Spinach Mushroom Breakfast Casserole

It’s a complete meal in one dish. With eggs, veggies, and cheese, you don’t need much else alongside it.
The goat cheese makes it special. It adds a tangy creaminess that pairs perfectly with the earthy mushrooms.
You can make it ahead. Assemble it the night before, then just bake in the morning, great for brunch hosting.

Key Ingredients for a Perfect Breakfast Casserole

Cremini mushrooms: Their earthy, slightly meaty flavor holds up well to egg baking. Slice them about ¼-inch thick so they cook evenly. Baby bellas are a fine substitute.
Fresh spinach: Use whole baby spinach leaves, they wilt down quickly. Avoid frozen unless you squeeze it dry; excess water makes the casserole weepy.
Goat cheese: Its tangy creaminess offsets the earthy vegetables. Crumble it while cold; it softens during baking. If you don’t like goat cheese, feta or shredded gruyère are good swaps.

Kitchen Tools for This Brunch Casserole

9x13-inch baking dish (glass or metal both work)
Large skillet (12-inch) for sautéing vegetables
Large mixing bowl and whisk
Chef’s knife and cutting board

Tips for Making the Best Spinach Mushroom Breakfast Casserole

Don’t skip sautéing the mushrooms over high heat, it browns them quickly and concentrates their flavor. When you add the spinach, let it just wilt; if you cook it too long, it will release water and make the casserole soggy. For the eggs, whisk them thoroughly with the milk so the texture is uniform. Pour the egg mixture slowly over the vegetables so it settles evenly, then top with the remaining goat cheese before baking.

Expert Advice for a Flawless Brunch Casserole

To test for doneness, jiggle the pan slightly, the center should be just set, not liquid. If you insert a knife near the center, it should come out clean. Let the casserole rest for a full 5 minutes after baking; this lets the eggs firm up so you get clean squares. If you’re doubling the recipe, use a larger pan (like 11×15) and expect a slightly longer baking time.

Variations for Your Goat Cheese Breakfast Casserole

For a non-vegetarian version, add ½ cup cooked crumbled bacon or sausage to the vegetable layer. If goat cheese isn’t your thing, swap it for crumbled feta or shredded sharp cheddar. You can also fold in ⅓ cup sun-dried tomatoes (drained and chopped) along with the spinach for extra tang. To make it dairy-free, use a plant-based milk and omit the cheese or use a vegan alternative.

What to Serve with Spinach Mushroom Breakfast Casserole

I like to serve this casserole with a side of fresh fruit, a simple bowl of berries or sliced melon balances the richness. For a heartier brunch, add roasted potatoes or a warm crusty baguette with butter. A small green salad with lemon vinaigrette also works nicely if you’re serving it for lunch.

Storing Leftover Egg Casserole with Spinach and Mushrooms

Leftovers keep well in the refrigerator for up to 4 days. Cool the casserole completely, then cover the dish tightly with plastic wrap or aluminum foil, or transfer portions to an airtight container. Reheat as directed above.

Freezing This Vegetarian Breakfast Casserole

You can freeze either the unbaked assembled casserole or leftovers. For unbaked, assemble in a freezer-safe dish (skip the goat cheese topping; add it just before baking), cover tightly, and freeze for up to 3 months. Thaw overnight in the fridge, then bake as directed, adding 15-20 minutes. For baked leftovers, wrap individually in plastic wrap then foil, and freeze for up to 3 months. Reheat straight from frozen in a 350°F oven for 20-25 minutes.

How to Reheat Spinach Mushroom Breakfast Casserole

The best way to reheat leftovers is in a 350°F oven for about 10 minutes, this keeps the eggs fluffy and the edges crisp. If you’re in a hurry, the microwave works too: heat a single portion on high for 45-60 seconds, but expect a softer texture. For a large batch, cover the dish with foil and reheat at 325°F for 15-20 minutes until warmed through.